Thermosetting adhesives and pressure-sensitive adhesives are used in a variety of applications with elevated fire/flame risk (e.g., aircraft, cars, trains, ships, electrical wiring, and electronics). These adhesives are typically combustible and/or flammable unless one or more flame retardant is added to reduce the fire/flame risk.
Flame retardants may reduce the flammability of materials by one or more of a variety of mechanisms including, for example, quenching free radicals in the gas phase, reacting with chemical fragments from the burning material to initiate char formation, and forming barrier layers within the burning material.
Commonly used flame retardants include halogenated compounds such as polychlorinated biphenyl and polybrominated diphenyl ethers. These flame retardants are well-known and very efficient at fire retardation in combustible materials. However, many compounds in this class of flame retardants are considered hazardous substances. Several of the most effective halogenated flame retardants have been banned by the European Union under the Restriction of Hazardous Substances (RoHS) since Jul. 1, 2006. Several Asian countries and individual states in the United States are also following with similar RoHS directives. In addition, an increasing number of end-product manufacturers are establishing policies to refuse to use halogenated flame retardant materials in their products. Accordingly, there is a continuing need for new halogen-free flame retardants.